A standard gear-change transmission has a housing, typically of cast aluminum, in which are provided input, output, and counter shafts, typically of machined steel. The input and output shafts are coaxial and the countershaft is parallel to but spaced from the input/output-shaft axis. Four housing bearings support the input-shaft front end, output-shaft rear end, and both ends of the countershaft in the housing and a fifth bearing supports the front end of the output shaft on the rear end of the input shaft. In the standard synchromesh transmission gears that are in continuous mesh are provided on the shafts and various clutches can be closed to establish the speed ratio between the input shaft and the output shaft.
A main problem in such arrangements is that the coefficients of thermal expansion are different for the aluminum housing and the steel shafts. The result is that bearings that are perfectly centered when the transmission is constructed and generally at room temperature will become too tight or too loose when the transmission heats up, which it does invariably in use.
In German patent 3,417,699 issued 15 Oct. 1987 to H. Bender this differential-expansion problem is solved by making the countershaft and output shaft as two-part telescoping structures including a thermal-expansion element whose own expansion is such that the respective shafts will expand and contract the same as the housing. While relatively effective, this system nonetheless requires that the five bearings be meticulously fitted and in general the construction of this thermal-compensated transmission is quite expensive.